1. Field of the Invention
This invention relates generally to the field of optical sights, such as arc found in military weapon systems. More particularly, the invention relates to a module that retrofits onto an existing optical sight and provides both an optical sight channel for a gunner operating the weapon and a video channel for conveying the image that the gunner sees through the eyepiece to a port for transmission to a commander or other user at a remote location.
2. Description of Related Art
It is well known in the art to provide a sighting system for a weapon, such as a surface-to-surface or surface-to-air missile. The sighting system typically presents at an eyepiece a missile aiming mark indicating the boresight of the weapon superimposed on the field-of-view of the sight, as well as fire control or missile status information. More recent sights have been developed that incorporate an electronics module and cathode ray tube (CRT), in which the image on the surface of the CRT is also superimposed for view through the eyepiece. The information displayed on the CRT may be virtually anything, including ballistics information, imagery used for training purposes such as enemy tanks or aircraft, etc. Some sighting systems also include laser range finding units and thermal imaging modules that present range and thermal images of the scene to the gunner at the eyepiece.
Prior art sighting systems are described in U.S. Pat. No. 5,530,246 to Hawkins, U.S. Pat. No. 3,997,762 to Ritchie et al., U.S. Pat. No. 4,777,861 to Lecuyer et al., assigned to the assignee of the present invention, and U.S. Pat. No. 5,129,309 also to Lecuyer et al. and assigned to the assignee of the present invention. Each of the above patents is fully incorporated by reference herein.
The above sighting systems are all integrated, stand-alone sighting systems and are not retrofit systems per se, i.e., adapted to be installed in a retrofit fashion on a preexisting optical system. Retrofit sighting systems are known in the art, however, and have been developed by the Applicants' assignee. This prior art system is shown schematically in FIG. 1. With the retrofit vision module 10, prior to installation the sight eyepiece 12 is removed from the sighting system unit 14, and an adapter plate 16 is installed on the unit 14. The vision module 10 is installed on the adapter plate 16 and then the eyepiece 12 is installed on the vision module 10. The vision module includes the main optical channel 20, a beam combining prism arrangement which may be accomplished with a multi-component prism assembly 24, and a second or CRT channel 26. The vision module 10 provides to the gunner at the eyepiece 12 a replica image of the main sight unit image and a superimposed CRT image.
The present invention provides for a more expanded capability than prior art retrofit systems and allows the module to meet more comprehensive military requirements. In addition, by adding the capability of generating a video image of the view seen by the gunner, new possibilities for use of the sighting system and weapon system are presented.
In particular, the present invention provides the gunner with a view of the main sight image from the first channel and a second view, from a second or "CRT" channel, which can be a reticle, a natural picture or scene, or a programmed training image. The nature of the second image in the CRT channel is essentially unlimited. In a normal mission using a prior art sighting system, the gunner can, for example, utilize a special reticle provided in the module for gunnery purposes. However, the commander cannot see the same view which the gunner sees. In an important advantage of the present system, the video channel in the vision module is coupled to a port that conveys a video image of what the gunner sees to the commander so that he can override the gunner's action, if necessary. The commander sees the same view as that of the gunner on a suitable display, such as on a head-mounted display or a flat panel display. The commander override may prevent, for example, casualties due to a friendly fire situation.
The feature of porting the image the gunner sees to the commander has other potential uses besides fire control. For example, the weapon and sighting system may be used for training exercises, with the video of the image the gunner sees used to monitor and help improve the performance of the gunner. In this example, predetermined training imagery may be introduced into the CRT channel and the ability of the gunner to track targets in the training imagery and operate the fire mechanisms for the weapon may be evaluated live or recorded for later evaluation or critique.
In yet another aspect of the invention, the luminous source in the second channel may be a color liquid crystal display (LCD) instead of a CRT. Small CRTs, although they offer a bright image, cannot produce colored imagery without significant loss of resolution. LCD technology offers full-color display of good resolution imagery but at reduced luminance. The LCD image may be highly diluted when superimposed upon a bright main image in the first channel. To overcome this, the invention provides for a variable optical density device or filter in the first optical channel. One example of such a variable optical density filter is an optical glass wheel with varying levels of optical density in the azimuthal direction but constant optical density in the radial direction. Rotation of such a wheel can vary the effective transmission through the main image channel thereby adjusting the relative luminance of the main image versus the LCD image and offer good visibility. Further, the use of such a wheel with a very high optical density region can act as a mechanical shatter. Both the wheel or the shutter, if employed, can also have fail-safe features which allow the images to be seen even if electrical power to the vision module fails.